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due the complicated patterns upon the grinding teeth of Ungulates,
which are produced by the wearing away of the dentine and the
cement, and the resistance of the enamel.
The centre of the tooth papilla remains soft and forms the
pulp of the tooth, which is continuous with the underlying
tissues of the gum by a fine canal or a wide cavity as the case
may be. In teeth which persistently grow throughout the life-
time of the animal, as for example the incisors of the Eodents,
there is a wide intercommunication between the cavity of the
tooth and the tissues of the gum; only a narrow canal "exists in,
for instance, the teeth of Man, and in fact in the vast majority
of cases. The three constituents of the typical teeth are not,
however, found in all mammals; the layer which is sometimes
wanting is the enamel. This is the case with most Edentates;
but the interesting ' discovery has been made (by Tomes) that in
the Armadillo there is a downgrowth of the epidermis similar to
that which forms the enamel in other mammals, a rudimentary
*' enamel organ."
Teeth are present in nearly all the Mammalia; and where
they are absent there is frequently some evidence to show that
the loss is a recent one. The Whalebone Whales, the Mono-
tremata, Manis, and the American Anteaters among the Edentata
are devoid of teeth in the adult state. In several of these
instances, however, more or less rudimentary teeth have been
found, which either never cut the gums or else become lost
early in life. The latter is the case with Ornithorliynchus,
where there are teeth up to maturity (see p. 113). Ktikenthal
has found germs of teeth in Whales, and Hose in the Oriental
Manis. The loss of the teeth in these cases seems to have
some relation to the nature of the food. In ant-eating
mammals, as in the Anteaters and Echidna, the ants are
licked up by the long and viscid tongue, and require no
mastication. Yet it must be remembered that Qrycteropus is
also an anteater, like the Marsupial Myrmecobius, both of which
genera have teeth.
The first of the essential peculiarities of the mammalian
teeth as compared with those of other vertebrates concerns the
position of the teeth in the mouth. There is no undoubted
mammal extinct or living in which the teeth are attached to
any bones other than the dentary, the maxilla, and the pre-